Reciprocating Pump

ABSTRACT

A reciprocating pump ( 10 ) for pumping seawater or other fluid under high-pressure. The pump ( 10 ) has a pump body ( 11 ) defining an internal space ( 13 ) and an opening ( 18 ) onto the internal space. A plunger ( 25 ) extends through the opening ( 18 ) and into the internal space ( 13 ). A sheath ( 30 ) closes the opening ( 18 ) and embraces an inner portion of the plunger ( 25 ), whereby pumping chamber ( 33 ) is defined between the pump body ( 11 ) and the sheath ( 30 ). The sheath ( 30 ) is deformable in response to reciprocatory movement of the plunger ( 25 ) to effect volume change within the pumping chamber ( 33 ). The sheath ( 30 ) comprises a first portion ( 31 ) which is generally stable, and a second portion ( 32 ) which embraces the plunger ( 25 ) and which deforms through expansion and contraction upon reciprocatory movement of the plunger. The first portion ( 31 ) defines a mounting flange ( 35 ) clampingly engaged with the pump body ( 11 ). The sheath ( 30 ) incorporates a recess ( 45 ) adjacent the open end thereof. A reinforcement sleeve ( 47 ) is located in the recess ( 45 ), whereby a cavity is defined between the reinforcement sleeve ( 47 ) and the plunger ( 25 ). There is also provision for lubricating the interface between the sheath ( 30 ) and the plunger ( 25 ).

FIELD OF THE INVENTION

This invention relates to a reciprocating pump.

The invention has been devised particularly for pumping seawater at high pressure. It should, however, be understood that the invention may also find application for pumping of various fluids other than seawater.

BACKGROUND ART

In International Application PCT/AU03/00813, there is a proposal for harnessing wave energy and converting the wave energy to pressurised fluid for use in any appropriate way. In a typical application, the fluid comprises seawater drawn from the ocean environment in which the apparatus operates. The seawater is pumped under high pressure to shore for utilisation there.

Pumping of seawater at high pressure, possibly in excess of 70 Bar, utilising a reciprocating pump powered by wave energy (and thus likely to have a relatively slow moving, variable stroke) can present technical difficulties.

A pump exposed to difficult operational conditions, such as pumping of seawater at high pressure, may require the various attributes. The pump may, for example, require the ability to handle corrosive or other aggressive fluids (such as seawater) over an extended service life. Further, the pump may require the ability to operate with irregular and non-sinusoidal strokes (as may be produced from a drive train powered directly by a renewable energy source such as wave motion). There may also be a need to tolerate a degree of misalignment (i.e. tilting of the piston axis). It may also be desirable that the pump be relatively easy to maintain (for example, easy to lubricate). Further, relatively low mechanical dissipation (i.e. relatively high efficiency) would be particularly advantageous.

The present invention seeks to provide a pump capable of meeting at least one of the attributes specified above.

DISCLOSURE OF THE INVENTION

According to one aspect of the invention there is provided a reciprocating pump comprising a body defining an internal space and an opening onto the internal space, an operating element extending through the opening and into the internal space, a sheath closing the opening and embracing an inner portion of the operating element, a pumping chamber defined between the body and the sheath, the sheath being deformable in response to reciprocatory movement of the operating element to effect volume change within the pumping chamber, and a cavity about the operating element adjacent the open end of the sheath.

The cavity may serve one or more purposes. The cavity may, for example, provide a reservoir for lubricant. In addition, or alternatively, the cavity may assist in accommodating angular misalignment of the operating element.

Typically, the cavity comprises an annular cavity.

Preferably, the cavity is defined between the periphery of the operating element and a surrounding surface.

In one arrangement, the surrounding surface may be defined by a reinforcement sleeve formed separately of the sheath and located in a recess within the sheath.

In another arrangement, the surrounding surface may be defined by the open end portion of the sheath. In such an arrangement, the open end portion of the sheath may incorporate reinforcement for maintaining the end in an open condition spaced from the operating element, whereby the cavity comprises the space between the open end portion of the sheath and the operating element. The reinforcement may comprise a reinforcement ring incorporated into the sheath.

The cavity may be closed at the outer end thereof by a seal such as a wiper seal.

The operating element may be configured as a plunger.

The open end of the sheath may be configured to provide a mounting flange.

The sheath may comprise a first portion which is generally stable and which preferably provides the mounting flange, and a second portion which embraces the plunger and which deforms through expansion and contraction upon reciprocatory movement of the plunger.

Preferably, the cavity is accommodated within the confines of the first portion.

The second portion may comprise a surface which confronts the plunger. The surface of the shroud second portion confronting the plunger may be configured to accommodate lubricant.

The configuration of the surface for accommodating lubricant may comprise formations on the surface. The formations may create interstices in which lubricant can be trapped. The formations may be of any appropriate form, such as knobs, ridges or other protrusions, or alternatively dimples.

The lubricant may be any substance that reduces the sliding friction between the outer surface of the plunger and the inner surface of the sheath so that there is uniform sliding between the two surfaces without striction.

The lubricant may, for example, comprise seawater itself, silicon grease, castor oil, brake fluid and polypropylene glycol.

The outer surface of the plunger may be coated with an appropriate low-friction material, such as polytetrafluoroethylene.

There may be provision for lubricant to be fed within the sheath. Such provision may include formations on the inner surface of the sheath. The lubricant may be so fed either under gravity or under pressure.

In one arrangement, lubricant can be fed to the region adjacent the inner end of the sheath. This can be done by way of a lubricant delivery path in the operating element.

According to a second aspect of the invention there is provided a reciprocating pump comprising a body defining an internal space and an opening onto the internal space, an operating element extending through the opening and into the internal space, a sheath closing the opening and embracing an inner portion of the operating element, a pumping chamber defined between the body and the sheath, the sheath being deformable in response to reciprocatory movement of the operating element to effect volume change within the pumping chamber, a recess in the sheath adjacent the open end thereof, a reinforcement sleeve located in the recess, whereby a cavity is defined between the reinforcement sleeve and the operating element.

According to a third aspect of the invention there is provided a reciprocating pump comprising a body defining an internal space and an opening onto the internal space, a plunger extending through the opening and into the internal space, a sheath closing the opening and embracing an inner portion of the plunger, a pumping chamber defined between the body and the sheath, the sheath being deformable in response to reciprocatory movement of the plunger to effect volume change within the pumping chamber, the sheath comprising a first portion which is generally stable and a second portion which embraces the plunger and which deforms through expansion and contraction upon reciprocatory movement of the plunger, the first portion defining a mounting flange clampingly engaged with the body.

According to a fourth aspect of the invention there is provided a reciprocating pump comprising a body defining an internal space and an opening onto the internal space, a plunger extending through the opening and into the internal space, a sheath closing the opening and embracing an inner portion of the plunger, a pumping chamber defined between the body and the sheath, the sheath being deformable in response to reciprocatory movement of the plunger to effect volume change within the pumping chamber, and feed means for feeding lubricant into the region between the plunger and the sheath.

According to a fifth aspect of the invention there is provided a sheath comprising a first portion defining a mounting flange and a second portion adapted to embrace a plunger received within the sheath, the second portion being adapted to expand and contract upon reciprocatory movement of the plunger.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the following description of several specific embodiments thereof as shown in the accompanying drawings in which:

FIG. 1 is a schematic perspective view of a reciprocating pump according to a first embodiment;

FIG. 2 is a sectional elevational view of the pump of FIG. 1;

FIG. 3 is a sectional side elevational view of the pump of FIG. 1;

FIG. 4 is a fragmentary view, on an enlarged scale, illustrating an arrangement of parts between the pump plunger and the pump body;

FIG. 5 is a sectional elevational view of the pump body;

FIG. 6 is a schematic perspective view of a sheath forming part of the pump;

FIG. 7 is a side view of the sheath;

FIG. 8 is a fragmentary view illustrating part of the sheath on an enlarged scale;

FIG. 9 is a side elevational view of an upper part of the pump plunger;

FIG. 10 is a perspective view of a lower part of pump plunger;

FIG. 11 is a sectional elevational view of the lower plunger part;

FIG. 12 is a fragmentary view, on an enlarged scale, of one end of the plunger, illustrating a diffuser accommodated therein;

FIG. 13 is a sectional elevational view of the diffuser;

FIG. 14 is a schematic perspective view of diffuser;

FIG. 15 is a schematic elevational view of a sheath for a pump according to a second embodiment; and

FIG. 16 is a fragmentary view illustrating part of the sheath of FIG. 15.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Referring to FIGS. 1 to 14 of the drawings, there is shown a reciprocating pump 10 according to a first embodiment which is particularly suitable for pumping seawater under high pressure. The seawater is drawn from the ocean itself and so is at an initial pressure corresponding to the hydrostatic pressure at the ocean depth from which the seawater is drawn.

Where the pump 10 is powered by wave energy, it typically operates with a slow-moving, variable stroke. The pump is of a construction particularly suited to such an application.

The pump 10 comprises a body 11 configured as a cylindrical pressure vessel defining an internal space 13. The body 11 comprises a cylindrical side wall 15 and an end wall 17 at one end of the cylindrical side wall 15. The end wall 17 has an opening 18 therein. The other end of the cylindrical side wall 15 is closed by a base 19.

The end wall 17 is defined by an end plate 20 detachably connected to the cylindrical side wall 15, the detachable connection in this embodiment being provided by machine screw fasteners.

The pump 10 further comprises an operating element 23 comprising a plunger 25 having a cylindrical side face 26 and an end face 27. The plunger 25 is attached to a connector 28 adapted to undergo reciprocatory motion under the influence of a drive train powered, for example, by wave motion. In this embodiment, the connector 28 is configured as a hinge bush which receives a hinge pin 29 connected to a lever (not shown), whereby reciprocation of the lever imparts reciprocation motion to the plunger 25.

The plunger 25 extends into the internal space 13 through the opening 18 within the end wall 17.

A sheath 30 is mounted on the body 11 about the opening 18 for embracing that portion of the plunger 25 extending into the internal space 13. The sheath 30 is made of an elastomeric material, preferably rubber.

The sheath 30 is attached to the body 11 to close the opening 18, whereby a pumping chamber 33 is defined between the sheath 30 and the body 11. The sheath 30 provides a deformable boundary surface for the pumping chamber 33, whereby deformation of the boundary surface effects a change of volume of the pumping chamber 33.

The body 11 incorporates an inlet 12 and an outlet 14, both of which communicate with the pumping chamber 33.

The sheath 30 comprises a first portion 31 and a second portion 32, with the two portions being formed integrally. The first portion 31 is substantially rigid in the sense that it does not undergo significant deformation during operation of the pump. The second portion 32 embraces the plunger 25 and is adapted to undergo extension and contraction during operation of the pump.

The first portion 31 is configured to provide a mounting flange 35. The second portion 32 is of generally tubular construction, involving a tubular wall section 36 and an end section 37, with the flange 35 provided by the first portion 31 being at one end of the tubular wall section 36 and the other end of the tubular wall section being closed by the end section 37.

The mounting flange 35 defined by the first portion 31 is secured to the body 11 through clamping engagement between the end wall 17 and an annular seat 38. The seat 38 is defined by a seat element 39 mounted on an annular shoulder 40 provided internally on the cylindrical side wall 15 inwardly of the end wall 17.

The mounting flange 35 has an outer end face 41 for bearing against end wall 17 and an inner end face 43 for bearing against seat 38 in sealing engagement therewith.

The first portion 31 further includes an annular recess 45 which opens onto outer end face 41. The recess 45 is adapted to receive a reinforcement sleeve 47. The reinforcement sleeve 47 is of annular construction, having an inner face 49 which defines a central opening of diameter larger than the diameter of the plunger 25. In this way, a gap 51 is defined between the sleeve 47 and the plunger 25.

The reinforcement sleeve 47 is of rigid construction, being made of steel in this embodiment. The reinforcement sleeve 47 serves to provide reinforcement for the flange and more particularly maintain the presence of the gap 51.

The purpose of the gap 51 is to provide a cavity for accommodating a lubricant. The lubricant may be any liquid that reduces the sliding friction between the outer surface of the plunger 25 and the inner surface of the sheath.

Additionally, the gap 51 provides some clearance space for accommodating any slight misalignment of the plunger 25 with respect to the body 11.

Further, the reinforcement sleeve 47 serves to exert an outward radial force on the flange 35 when the latter is compressed by the clamping engagement between the mounting flange 35 and the seat 38, thereby ensuring that a high pressure seal is formed between the sheath 30 and the body 11. More particularly, the radial force exerted by the sleeve 47 serves to ensure that there is a high pressure seal established between the inner face 43 of the flange and the annular supporting seat 38.

The reinforcement sleeve 47 has a recess 52 on the inner face thereof which receives a wear band 53 for sliding contact with the outer surface of the plunger 25. The wear band 53 thus projects beyond the inner face of the reinforcement sleeve 47, as shown in the drawings. The wear band 53 does not fully occupy the gap 51 so that the latter can perform its intended purpose.

A wiper seal 55 is accommodated between the reinforcement sleeve 47 and the end plate 20. The wiper seal 55 is in sliding engagement with the plunger 25 and is provided for the purposes of inhibiting loss of lubricant as the plunger executes its reciprocatory motion.

The outer surface of the plunger 25 may be coated with an appropriate non-sick material.

While not shown in the drawings, the pump 10 also comprises a suitable arrangement of valves for controlling the direction of fluid flow through inlet 12 into the pumping chamber 33 and out of the pumping chamber 33 through outlet 14.

The second portion 32 of the sheath 30 is shaped to follow the contour of the plunger 25 so that the extension of the sheath occurs primarily in the tubular wall portion 36 thereof. This results in a thinning down of the tubular wall portion 36 as the plunger 25 moves inwardly during a pumping stroke, stretching the elastomer material. The pressure generated by the seawater during a pumping cycle will generally be isostatic if the fluid velocities around the sheath are low (which they will be) so the fluid force acts to keep the sheath in contact with the plunger 25. This assists in maintaining the durability and service life of the sheath by preventing the formation of folds or local areas of enhanced fibre stress. The plunger 25 provides a surface which affords lateral support to the tubular wall section 36, as well as the end section 37, as they are subjected to high fluid pressure.

Where the elastomeric material forming the sheath is natural rubber, and where the pump is employed for pumping of seawater as alluded to above, it is estimated that up to 2 mm of surface of the rubber in contact with the water will abrade over a period of say 20 years. In such an instance, it is important that the sheet thickness be made large enough to accommodate this reduction over the usable lifetime of the pump.

The sheath 30 incorporates ribbing 61 on its internal surface in the region below recess 45 to allow lubricant to feed under the influence of gravity from the lubricant reservoir provided by gap 51 downwardly to other parts of the sheath. The downward flow of lubricant may also be assisted by making the internal diameter of the second portion 32 of the sheath 30 slightly greater than the outside diameter of the plunger so that there is some clearance at least during the initial part of the intake stroke of the pumping cycle when the pressure of fluid being pumped is not yet high enough to force this clearance to zero.

The plunger 25 incorporates an axial passage 71 extending to the end face 27 thereof for delivery of lubricant thereto. The passage 71 receives lubricant from an external source. With this arrangement, lubricant can be delivered to the region adjacent the inner end of the sheath 30; that is, to the interface between the plunger end face 27 and sheath end section 37.

The lubricant may comprise a continuous flow of lubricant material (such as seawater) flowing downwardly along the passage 71, and then upwardly between the cylindrical face 26 of the plunger 25 and the tubular wall portion 36 of the sheath. With this arrangement, any surplus lubricant can simply flow from the sheath 30 through the open end thereof.

In this embodiment, the lubricant comprises seawater which is sourced from the high-pressure seawater delivered by the pump. This is accomplished by way of a bypass line 75 extending from the pump outlet 14 to the axial passage 71, as best seen in FIGS. 1 and 2 of the drawings. The bypass line 75 of course needs to be flexible or otherwise constructed in order to accommodate movement of the plunger 25 relative to the pump body 11 with which the outlet 14 is formed. A valve 77, which in this embodiment comprises a needle valve, is associated with the bypass line 75 for regulating the supply of high-pressure seawater from the pump outlet 14 to the axial passage 71.

The plunger 25 comprises a first part 81 which includes a head section 83 attached to the connector 28 and a tube 85 extending downwardly from the head section 83. The plunger 25 further comprises a second part 87 adapted to fit onto the first part 81 in order to provide the cylindrical side face 26 and the end face 27 of the plunger. The second part 87 is of a generally cylindrical form, having a cylindrical sidewall portion 91 and an end wall portion 93. The end wall portion 93 incorporates an opening 95 into which the tube 85 locates when the second part 87 is fitted on to the first part 81. The opening 95 is configured to receive a diffuser 97. The diffuser 97 threadingly engages with the tube 85. The diffuser 97 has a diffuser passage 99 which communicates with the tube 85 to receive seawater delivered along the tube and diffuse it from the plunger.

A deflector plate 101 is incorporated into the sheath 30 to confront the diffuser 97. In this way, seawater delivered through the diffuser 95 impacts upon the deflector plate 101 which then distributes the seawater within the interface between the plunger 25 and the sheath 30.

Referring now to FIGS. 15 and 16 of the drawings, there is shown a sheath 30 for a pump according to a second embodiment. The pump according to the second embodiment is similar in many respects to the first embodiment and so corresponding reference numerals are used to identify like parts. In this embodiment, the sheath 30 is constructed in a similar fashion to the sheath for the first embodiment, with the exception that formations 105 are provided on the inner face 107 of the second portion 32 of the sheath, confronting the adjacent face 26 of the plunger 25. The formations 105 are configured to define interstices 111 for accommodating lubricant. In this embodiment, the formations 105 comprise an array of protrusions 109 between which there are defined spaces 113 which provide the interstices 111 for accommodating lubricant. The spaces 113 may allow the lubricant to migrate about the interface between the plunger 25 and the sheath 30, particularly at the stages during the pumping cycle where the sheath 30 is not pressed firmly into engagement with the confronting surface 26 of the plunger. At the stage where the fluid pressure within the pumping chamber 33 is at a level that the second portion 32 of the sheath 30 is pressed firmly into engagement with the confronting surface 26 of the plunger 25, the formations 105 cooperate to create pockets or zones which trap the lubricant in position, thereby ensuring that there is some lubricant at the interface between the second portion 32 of the sheath 30 and the plunger 25.

In certain pump applications, it may be possible to rely upon lubrication by way of gravity feed from the gap 51 and also .by way of the formations 105, without the need for lubricant delivery through the plunger.

In another embodiment, which is not shown, the end section 37 of the second portion 32 of the sheath 30 may be attached to the end face of the plunger 25. The attachment may be provided by way of a fastener, with the sheath end section 37 being clamped between the end face 27 of the plunger 25 and a clamping plate through which the fastener extends for attachment to the plunger. Such attachment would ensure that the sheath 30 is always withdrawn along with the return (outward) stroke of the plunger 25. It would, of course, be necessary to ensure that adequate fluid sealing is established around the fastener, whereby the integrity of the sheath is not compromised.

From the foregoing, it is evident that the present embodiments provide a simple yet highly effective pump which can perform in harsh environments. This is because working surfaces of the pump to which the seawater is exposed during pumping cycles are surfaces of the pump body 11 and the sheath 30 accommodated therein. Because of its construction, the pump is able to operate with the irregular and non-sinusoidal strokes arising from a drive system powered by wave energy. Further, because of the manner in which the plunger 25 is supported within the pump body 11, a degree of misalignment between the plunger 25 and the pump body 11 can be tolerated. The flexible nature of the sheath 30, at both the first and second portions 31, 32 thereof, assists in providing this tolerance.

It should be appreciated that the scope of the invention is not limited to the scope of the embodiments described. For example, while the pumps according to the embodiments have been described in relation to pumping of seawater, a pump according to the invention may find application in the pumping of various other fluid materials, including liquids, gases and slurries.

Modifications and changes can be made without departing from the scope of the invention.

Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 

1. A reciprocating pump comprising a body defining an internal space and an opening onto the internal space, an operating element extending through the opening and into the internal space, a sheath closing the opening and embracing an inner portion of the operating element, a pumping chamber defined between the body and the sheath, the sheath being deformable in response to reciprocatory movement of the operating element to effect volume change within the pumping chamber, and a cavity about the operating element adjacent the open end of the sheath.
 2. An reciprocating pump according to claim 1 wherein the cavity comprises an annular cavity.
 3. An reciprocating pump according to claim 1 wherein the cavity is defined between the periphery of the operating element and a surrounding surface.
 4. An reciprocating pump according to claim 3 wherein the surrounding surface is defined by a reinforcement sleeve located in a recess within the sheath.
 5. An reciprocating pump according to claim 4 wherein the reinforcement sleeve supports a wear ring in sliding engagement with the operating element.
 6. A reciprocating pump according to claim 3 wherein the surrounding surface is defined by the open end portion of the sheath.
 7. A reciprocating pump according to claim 6 wherein the open end portion of the sheath incorporates reinforcement for maintaining the end in an open condition spaced from the operating element.
 8. An reciprocating pump according to claim 1 wherein the cavity is closed at the outer end thereof by a seal.
 9. A reciprocating pump according to claim 1 wherein the operating element is configured as a plunger.
 10. A reciprocating pump according to claim 1 wherein the open end of the sheath is configured to provide a mounting flange.
 11. A reciprocating pump according to claim 1 wherein the sheath comprises a first portion which is generally stable, and a second portion which embraces the plunger and which deforms through expansion and contraction upon reciprocatory movement of the plunger.
 12. A reciprocating pump according to claim 11 wherein the first portion provides the mounting flange.
 13. A reciprocating pump according to claim 11 wherein the cavity is accommodated within the confines of the first portion.
 14. A reciprocating pump according to claim 11, wherein the second portion comprises a surface which confronts the plunger.
 15. A reciprocating pump according to claim 14 wherein said surface is configured to accommodate lubricant.
 16. A reciprocating pump according to claim 15 wherein the configuration of the surface for accommodating lubricant comprises formations on the surface.
 17. A reciprocating pump according to claim 9 wherein the outer surface of the plunger is coated with a low-friction material, such as polytetrafluoroethylene.
 18. A reciprocating pump according to claim 19 further comprising feed means for lubricant to be fed within the sheath.
 19. A reciprocating pump according to claim 18 wherein the feed means delivers lubricant to the region adjacent the inner end of the sheath.
 20. A reciprocating pump according to claim 19 wherein the feed means comprises a lubricant delivery path in the operating element.
 21. A reciprocating pump comprising a body defining an internal space and an opening onto the internal space, an operating element extending through the opening and into the internal space, a sheath closing the opening and embracing an inner portion of the operating element, a pumping chamber defined between the body and the sheath, the sheath being deformable in response to reciprocatory movement of the operating element to effect volume change within the pumping chamber, a recess in the sheath adjacent the open end thereof, a reinforcement sleeve located in the recess, whereby a cavity is defined between the reinforcement sleeve and the operating element.
 22. A reciprocating pump according to claim 21 wherein the reinforcement sleeve supports a wear ring in sliding engagement with the operating element.
 23. A reciprocating pump according to claim 21 wherein the cavity is closed at the outer end thereof by a seal.
 24. A reciprocating pump comprising a body defining an internal space and an opening onto the internal space, a plunger extending through the opening and into the internal space, a sheath closing the opening and embracing an inner portion of the plunger, a pumping chamber defined between the body and the sheath, the sheath being deformable in response to reciprocatory movement of the plunger to effect volume change within the pumping chamber, the sheath comprising a first portion which is generally stable and a second portion which embraces the plunger and which deforms through expansion and contraction upon reciprocatory movement of the plunger, the first portion defining a mounting flange clampingly engaged with the body.
 25. A reciprocating pump according to claim 24 wherein a recess is provided in the first portion of the sheath adjacent the open end of the sheath, and wherein a reinforcement sleeve is located in the recess whereby a cavity is defined between the reinforcement sleeve and the plunger.
 26. A reciprocating pump comprising a body defining an internal space and an opening onto the internal space, a plunger extending through the opening and into the internal space, a sheath closing the opening and embracing an inner portion of the plunger, a pumping chamber defined between the body and the sheath, the sheath being deformable in response to reciprocatory movement of the plunger to effect volume change within the pumping chamber, and feed means for feeding lubricant into the region between the plunger and the sheath.
 27. A reciprocating pump according to claim 26 wherein the feed means is adapted to deliver lubricant to the region adjacent the inner end of the sheath.
 28. A reciprocating pump according to claim 27 wherein the feed means comprises a lubricant delivery path in the plunger.
 29. A sheath for a reciprocating pump according to claim
 26. 30. A sheath comprising a first portion defining a mounting flange and a second portion adapted to embrace a plunger received within the sheath, the second portion being adapted to expand and contract upon reciprocatory movement of the plunger.
 31. A sheath according to claim 30 wherein the second portion comprises a surface adapted to confront the plunger, said surface being configured to accommodate lubricant.
 32. A sheath according to claim 30 further comprising a recess in the first portion adjacent the open end thereof, the recess being adapted to receive a reinforcement sleeve.
 33. (canceled)
 34. (canceled) 